EFFECTIVE FAULT ISOLATION METHODS TO IMPROVE 33kV NETWORK RELIABILITY A dissertation submitted to the Department of Electrical Engineering, University of Moratuwa in partial fulfillment of the requirements for the Degree of Master of Science S.M.M.S. WEERATUNA A IVERSITYS " ^ • • - • . ^ m . m i n i u r t( Wf Supervised by: Prof. H.Y.R. Perera ^ s n / / 6 2 A - 3 o r _ _ _ _ _ ^ Department of Electrical Engineering University of Moratuwa, Sri Lanka January 2009 University of Moratuwa 92963 T H 9*963 DECLARATION The work submitted in this dissertation is the result of my own investigation, except where otherwise stated. It has not already been accepted for any degree, and is also not being concurrently submitted for any other degree. S.M.M.S. Weeratunga I endorse the declaration by the candidate. Prof. H.Y.R. Perera i CONTENTS Page No. Declaration i Abstract iv-v Acknowledgement vi List of Tables vii List of Figures vi'i- 1. Introduction 1 1.1 Background 1 1.2 Reliability of33kV network of C.E.B 1 1.3 Motivation 2 2. Problem statement 3 2.1 Identification of the Problem 3 2.2 Objectives of the Study 3 2.3 Importance of the Study 3 3. Reliability analysis of 33kV network 4 3.1 Recloser event analysis 5 3.1.1 Re view of events 11 3.2 Type of faults 11 3.2.1 Transient fault 11 3.2.2 Permanent fault 3.3 Outage reduction method 13 3.3.1 Reduce faults in the network 13 3.3.2 Installation of fault indicators for remote indication 13 3.3.3 Remote operation of reclosers 14 3.3.4 Using line sectionalizing devices 14 3.4 Development model for reliability evaluation 15 4. An effective protection scheme reduce outage rate 19 4.1 Protection scheme of C.E.B 33kV network 19 4.1.1 Downstream protection scheme 21 4.2 Design new protection scheme 26 4.2.1 Design algorithm 26 4.2.2 Further mprovement 34 ii 4.3 Sample design 37 4.3.1 Calculation of shortcircut current 37 4.3.2 Calculation of eartfault current 39 4.3.3 Selection of recloser attempts to lockout 42 4.3.4 Selection of protection setting 43 4.3.5 Selection fuses for spurs at Kalumale feeder 51 4.4 Computer based model for new protection scheme 54 4.5 Advantages using new protection scheme 55 5. Conclusion and Recommendation 57 5.1 Improvement of reliability 57 5.2 Recommendation 58 5.2.1 Using event log of recloser 58 5.2.2 Reduce outage in the network 58 5.2.3 Isolating faulty line from the feeder 59 References 60 Appendix I, II & 111 iii ABSTRACT Improving reliability in power system is very important to the utilities as well as to the country as it is an important attribute of the supply quality and increases the end user satisfaction. The aim of this study is to investigate the fault identification and isolation techniques to improve reliability. This study focuses on the following; 1. Reliability status of 33kV network of C.E.B. 2. Type of faults in 33kV network and outage reduction methods. 3. Develop a mathematical model for reliability evaluation. 4. Analyze protection scheme of C.E.B 33kV network. 5. Design new protection scheme to reduce outages. The analyzed reliability indices of C.E.B are far below compared to internationally accepted levels. In this study reliability status of 33kV network is analyzed using event log data of reclosers and breakdown reports of Consumer Service Centers. The author is working at Region -04, C.E.B and two switching gantries of Region-04 are selected to analyze events one in wet zone and other in coastal zone. It can be seen that outage time and fault frequency are high during both monsoon periods, 86% of faults are line to earth, 67% of faults are of transient nature and the repair time in case of overcurrent fault is high due to poor workmanship in line connections. With this study predominant causes of faults in the network can be identified by using event log of recloser. The several methods for outage reduction are identified, installation of fault indicators for remote indication and remote operation of reclosers, using line sectionalize devices. iv The protection scheme of 33kV network is analyzed to find techniques to reduce outages. The downstream protective devices (fuse on Spurs) beyond the recloser do not distinguish permanent and transient faults. It can be seen nuisance fuse blowing in spurs as well as nuisance recloser lockout affecting all customers in feeder. A new protection scheme is designed to overcome the above problems. The developed method isolates unhealthy spurs from healthy sections, improves reliability and reduces maintenance cost and extent of unserved energy. ACKNOWLEDGEMENT First, I pay my sincere gratitude to Professor Ranjit Perera who encouraged and guided me to conduct this investigation and on perpetration of final dissertation. I also thank to Eng. J. Karunanayake who gave the valuable instructions during the study and valuable advice for perpetration of final dissertation. I would like to take this opportunity to extend my sincere thanks to Mr.U.K.W. Silva, Deputy General Manager (PHM-R4), Mr.L.TJ. Fernando, Deputy General Manger (Planning & Devlolopment-R4), Mr.S. Bogahawatta, Project Manager (Lightning Hambantota Project) Mr.S.T.S. Shantha (System Planning Engineer-Southern Province), Mr.K. Perera (System Planning Engineer-Rl), Mr.K. Wimalendra (Area Engineer-Kalutara), Mr.V.Ediriweera (Area Engineer-Matara), Mr.R. Thilakarathna (Electrical Superintendent - Agalawatta CSC), Mr.W.M. Premarathna (Electrical Superintendent-Dickella CSC) of Ceylon Electricity Board who gave their co- operation to conduct my investigation work successfully. It is a great pleasure to remember the kind co-operation extended by the colleagues in the post graduate programme, friends and specially my wife who helped me to continue the studies from start to end. vi List of tables Table number Description Table 1.1 Reliability statistics of 33kV C.E.B network Table 1.2 Reliability indices of 33kV C.E.B network Table 3.1 Rainfall data at Kithulgoda area Table 3.2 Rainfall data at Dickwella area Table 3.3 The occurrences of faults between lines and lines to earth Table 3.4 Average repair time of feeders Table 3.5 Recloser attempts of feeders Table 3.6 Types of faults at Kithulgoda Gantry Table 3.7 Types of faults at Dickwella Gantry Table 3.8 Assumed failure rates of feeder Table 3.9 Assumed consumers of feeder Table 3.10 Annual outage time when spurs connected directly to sections Table 3.11 Annual outage time when spurs connected with fuses and manual isolation Table 3.12 Annual outage time when spurs connected with fuses and sectionalizers Table 4.1 Connected fuse links at Kalumale feeder Table 4.2 Multiplying factor (k) for recloser curves Table 4.3 Connected fuse links in Kalumale feeder with new protection scheme Table 4.4 Reliability indices of Kalumale feeder Table 4.5 Annual requirement of fuse types of C.E.B vii List of figures Figure number Description Figure 3.1 Feeding arrangement of 33kV switching Gantry Figure 3.2 Outage period of feeders at Kithulgoda Gantry Figure 3.3 Reclosing of feeders at Kithulgoda Gantry Figure 3.4 Earthfault of feeder at Kihulgoda Gantry Figure 3.5 Overcurrent of feeders at Kithulgoda Gantry Figure 3.6 Outage period of feeders at Dickwella Gantry Figure 3.7 Reclosing of feeders at Dickwella Gantry Figure 3.8 Earthfault of feeder at Dickwella Gantry Figure 3.9 Overcurrent of feeders at Dickwella Gantry Figure 3.10 Spur lines connected directly to sections Figure 3.11 Spur lines connected across fuse with sections Figure 4.1 Protection scheme between GSS CB and Recloser Figure 4.2 Protection curves between GSS CB and Recloser Figure 4.3 Protection curves when spur line is protected by 10A fuse Figure 4.4 Protection curves when spur line is protected by 15A fuse Figure 4.5 Protection curves when spur line is protected by 20A fuse Figure 4.6 Protection curves when spur line is protected by 40A fuse Figure 4.7 Network diagram ' Figure 4.8 Algorithm for new protection scheme design Figure 4.9 Recloser to fuse miscoordination classification Figure 4.10 Recloser to fuse coordination curves viii Figure number Description Figure 4.11 Relay to fuse coordination curves Figure 4.12 Fuse to fuse miscoordination classification Figure 4.13 Fuse to fuse coordination of curves Figure 4.14 Relay to relay miscoordination classification Figure 4.15 Relay to relay coordination curves Figure 4.16 Sectionalizer device Figure 4.17 Sectionalizers in 33kV network Figure 4.18 Single line diagram of Kaumale feeder Figure 4.19 Overcurrent settings of protective devices with 50A fuse Figure 4.20 Earthfault settings of protective devices with 50A fuse Figure 4.21 Coordination of 50A (T type) fuse and 20A (K type) fuse Figure 4.22 The model for 33kV feeder to analyze protection coordination IX